1. Field of the Invention
The present invention relates to methods of attaching composite materials to metallic materials and, more particularly, to methods of attaching carbon composites to metallic structures and to products produced by such methods.
2. Description of the Related Art
Composite materials produced by embedding fibers in the form of staple, filament, or yarn in a matrix of plastic, metal, or ceramic have found many uses in engineering applications requiring high strength and low weight, as in aeronautics and astronautics. Fibers retaining high strength at elevated temperatures are valuable in high-temperature applications. Carbon and graphite fibers fall into this category. Because the element carbon has the ability to form strong bonds between its atoms, carbon atoms are capable of holding together in strings to form long unidimensional polymer structures in the same way that molecules from the basic structural units of fibers. The fibers used in textiles are based almost exclusively on organic polymers consisting of long chains of carbon atoms with other atoms or groups of atoms attached as appendages to the carbon "spine." By removing the appendages from an organic fiber molecule, long molecules consisting entirely of carbon atoms can be produced. When chemical stripping of the appendages is carried out on a highly oriented organic fiber, carbon fibers in which the molecules have a high degree of orientation can be obtained. Carbon fibers of this sort may be produced by subjecting organic fibers to pyrolysis. Carbon fibers are formed at lower temperatures; at higher temperatures the carbon atoms in the fiber are arranged in the crystalline form of graphite.
Carbon fibers have a high strength-to-weight ratio and retain high strength at temperatures at which other engineering materials suffer significant loss of strength. Composite materials containing carbon fibers have many uses in the construction of aircraft and spacecraft. They are used in deep-sea vessels, in heavy-duty bearings, in pressure containment chambers, and in making the compressor turbine blades in jet engines. In these applications it is often desirable to make strong joints between composite materials and metal structures. Some examples of the art related to methods of joining composite materials and metals are described briefly below.
U.S. Pat. No. 2,509,020 to Stauffer et al. relates to an improved electrical contact brush member having a carbonaceous material portion with a metal terminal clip member attached thereto by an improved securing arrangement. A bond between the terminal clip member and the brush member is obtained by forming a coating of low electrical resistance metal, such as copper, over the contacting surface of the brush member. The coating may be formed by spraying fine particles of molten copper over the surface of the member adapted to be engaged by the terminal member. An alloying metal such as tin or zinc is then applied over the surface of the terminal member and a further mechanical connection between the terminal and brush members is formed by welding a connector between them.
U.S. Pat. No. 2,509,021 to Settle relates to electrical contact members and an improved method of making them. In a variation of the above-described patent to Stauffer et al., a two-part rivet is welded together to join the brush member to the terminal member by the passage of an electrical current therethrough.
U.S. Pat. No. 2,996,401 to Welch et al. is directed to a method of making ceramic structures for electron tubes in which a metallizing layer is firmly bonded to the ceramic. The metallizing layer is prepared by mixing powdered manganese and titanium with a powdered metal selected from the group consisting of molybdenum and tungsten. The resulting composition is brushed, sprayed, printed or otherwise applied to the desired area of the ceramic and then fired in an atmosphere furnace.
U.S. Pat. No. 3,321,019 to Dmitroff et al. is directed to the construction and method of construction of the root end of helicopter blades made of plastic reinforced with woven fiberglass cloth. A series of thin metal shims, plates, or inserts are embedded in the plastic blade root extending parallel to the blade chord. At least one ply of plastic impregnated woven fiberglass cloth is positioned between the metal laminates and is adhesively bonded thereto and extends therefrom into the remainder of the blade. Blade retaining bolts pass through holes in the blade root perpendicular to the chord so that blade loads are transmitted into the metal plates in shear and are then transmitted into the retaining bolts and into the blade retaining means.
U.S. Pat. No. 3,862,488 to Pessell et al. relates to a method of making a ceramic-to-metal joint in which a metal is brazed to a molybdenum metallized ceramic after first coating the molybdenum with palladium. The palladium is preferably plated onto the molybdenum by a chemical displacement process.
U.S. Pat. No. 4,120,998 to Olez relates to a composite structure comprising a beam formed by inserting two stepped metal end caps of a graphite/epoxy B-staged tubular strut. Multidirectional and unidirectional fibers are subsequently laid up to provide a structure which is in turn cocured to result in a unitized composite winged trunnion structure.
U.S. Pat. No. 4,228,976 to Eiselbrecher et al. is directed to an air foil or wing connected to the body of an aircraft or spacecraft through a main connector comprising metal and non-metal components. Pressure bodies and tension loops are arranged in a metal grommet for introducing pressure and tension forces into the outer skin of the wing as well as into the internal structure of the wing box. The metal grommet is in turn centered to and integrated with a main connector bearing bushing.
U.S. Pat. No. 4,321,011 to Hori et al. relates to a fan assembly with a hub portion, blades, and a stem being formed of molded plastics and made integral with each other. The stem is connected to an output shaft by means of bolts, each of which passes through a bushing. The bushing has a knurled portion of its outer surface and is inserted in a hole of the stem. The periphery of the hole is melted by heating upon insertion of the bushing therein so as to insure the connection of the fan assembly to the output member. If a spacer is interposed between the stem and a flange of the bushing, the spacer is fixedly connected to the bushing.
U.S. Pat. No. 4,636,142 to Baranski relates to a fan apparatus with a plurality of blade assemblies each of which has a molded plastic blade with an attachment insert partially embedded therewithin. The exposed portion of each attachment insert is rigidly attached to a corresponding one of the arms of a fan spider.
Other examples of related art are contained in the related application Ser. No. 07/173,787, entitled "High-Temperature Tensile Test Specimen and Method of Fabrication" by W. N. Pratt, assigned to the assignee of the present invention, the contents of which application are incorporated herein by reference.
None of the patents briefly described above discloses a method for attaching electrically conductive composite structures, such as those of carbon, to metallic structures by forming a pocket configuration along with a hole for a fastening member by a molding operation and thereafter plating the pocket area along with the hole walls with a nickel layer so as to provide a high strength area, with the possibility of brazing a metal structure to the nickel-plated composite.